The U.S. Geological Survey, in cooperation with the National
Oceanic and Atmospheric Administration and the Connecticut Department
of Environmental Protection, has produced detailed geologic maps of the
sea floor in Long Island Sound, a major East Coast estuary surrounded
by the most densely populated region of the United States. These
studies have built upon cooperative research with the State of
Connecticut that was initiated in 1982. The current phase of this
research program is directed toward studies of sea-floor sediment
distribution, processes that control sediment distribution, nearshore
environmental concerns, and the relation of benthic community
structures to the sea-floor geology.
The bathymetry data in this data set were collected during 2003 for
charting applications as part of NOAA project OPR-B340-RU, survey
H11045 aboard the NOAA Ship RUDE. The RUDE, which supports NOAA's
east-coast nautical charting mission, is outfitted to acquire
single-beam bathymetry with an Odom Echotrac DF-3200 duel frequency
echosounder and shallow water multibeam bathymetry with a Reson 8125
system. The Reson multibeam system operates at 455 KHz with a 120
degree across track swath and 240 beams along its swath.

Planar coordinates are encoded using row and column
Abscissae (x-coordinates) are specified to the nearest 5.000000
Ordinates (y-coordinates) are specified to the nearest 5.000000
Planar coordinates are specified in meters

The horizontal datum used is D_WGS_1984.
The ellipsoid used is WGS_1984.
The semi-major axis of the ellipsoid used is 6378137.000000.
The flattening of the ellipsoid used is 1/298.257224.

The multibeam data for this survey was acquired in XTF
(extended Triton data format) and recorded digitally through an ISIS
data acquisition system. Once digitally recorded, the XTF data were
processed using CARIS HIPS/SIPS software to quality control the data
and to incorporate sound velocity and tidal corrections. Data were
gridded to 5 m; vertical datum is mean lower low water.

The original multibeam data sets, which are in ASCII
comma-delimited text, do not entirely cover the sea floor because line
spacing during acquisition was such that areas of no data often are
present between the ship's tracks. Therefore, further processing was
conducted at the USGS's Woods Hole Science Center to provide
bathymetric datasets with more continuous coverage. First, all
non-standardized records were assumed to be bad records and were
removed. Subsequently, the PROJ.4 cartographic projections library was
used to project the data, the SwathEd software produced by the Ocean
Mapping Group at the University of New Brunswick was used to create the
grids from the actual sounding data, and GMT (the Generic Mapping
Tools) was used to create a 3-m interpolated grid of the bathymetry.
Interpolation was achieved during GMT processing by running the data
through a block median filter and using a surface generating algorithm
with a tension of 0.5. Other parameters were set at default. The grid
was projected into Universal Transverse Mercator, Zone 18N.

Although this data set has been used by the USGS and
NOAA, no warranty, expressed or implied, is made by the USGS or NOAA as
to the accuracy of the data and/or related materials. The act of
distribution shall not constitute any such warranty, and no
responsibility is assumed by the USGS or NOAA in the use of these data
or related materials.